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Change signature of target_features_cfg.

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Currently it is called twice, once with `allow_unstable` set to true and
once with it set to false. This results in some duplicated work. Most
notably, for the LLVM backend, `LLVMRustHasFeature` is called twice for
every feature, and it's moderately slow. For very short running
compilations on platforms with many features (e.g. a `check` build of
hello-world on x86) this is a significant fraction of runtime.

This commit changes `target_features_cfg` so it is only called once, and
it now returns a pair of feature sets. This halves the number of
`LLVMRustHasFeature` calls.
This commit is contained in:
Nicholas Nethercote 2025-02-25 15:25:54 +11:00
parent 2df8e657f2
commit 936a8232df
6 changed files with 85 additions and 71 deletions
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13
compiler/rustc_codegen_cranelift/src/lib.rs
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@ -176,13 +176,9 @@ impl CodegenBackend for CraneliftCodegenBackend {
}
}
fn target_features_cfg(
&self,
sess: &Session,
_allow_unstable: bool,
) -> Vec<rustc_span::Symbol> {
fn target_features_cfg(&self, sess: &Session) -> (Vec<Symbol>, Vec<Symbol>) {
// FIXME return the actually used target features. this is necessary for #[cfg(target_feature)]
if sess.target.arch == "x86_64" && sess.target.os != "none" {
let target_features = if sess.target.arch == "x86_64" && sess.target.os != "none" {
// x86_64 mandates SSE2 support and rustc requires the x87 feature to be enabled
vec![sym::fsxr, sym::sse, sym::sse2, Symbol::intern("x87")]
} else if sess.target.arch == "aarch64" {
@ -196,7 +192,10 @@ impl CodegenBackend for CraneliftCodegenBackend {
}
} else {
vec![]
}
};
// FIXME do `unstable_target_features` properly
let unstable_target_features = target_features.clone();
(target_features, unstable_target_features)
}
fn print_version(&self) {